Humans define the groups to which they belong in abstract terms. Often they strive for lasting intellectual and emotional bonding with anonymous others, and make their greatest exertions in killing and dying not to preserve their own lives or to defend their families and friends, but for the sake of an idea—the transcendent moral conception they form of themselves, of “who we are.”

This is the “the privilege of absurdity; to which no living creature is subject, but man only’” of which Hobbes wrote inLeviathan. In The Descent of Man, Darwin cast it as the virtue of “morality … the spirit of patriotism, fidelity, obedience, courage, and sympathy” with which winning groups are better endowed in history’s spiraling competition for survival and dominance.

Across cultures, primary group identity is bounded by sacred values, often in the form of religious beliefs or transcendental ideologies, which lead some groups to triumph over others because of non-rational commitment from at least some of its members—to actions that drive success independent, or all out of proportion, from expected rational outcomes.

For Darwin himself, moral virtue was most clearly associated not with intuitions, beliefs, and behaviors about fairness and reciprocity, emotionally supported by empathy and consolation—which constitute nearly the entire subject matter of recent work in the philosophy, psychology, and neuroscience of morality—but with a propensity to what we nowadays call “parochial altruism”: especially extreme self-sacrifice in war and other intense forms of human conflict, where likely prospects for individual and even group survival had very low initial probability. Heroism, martyrdom, and other forms of self-sacrifice for the group appear to go beyond the mutualistic principles of fairness and reciprocity.

Whether for cooperation or conflict, sacred values, like devotion to God or a collective cause, signal group identity and operate as moral imperatives that inspire non-rational exertions independent of likely outcomes. In interviews, experiments, and surveys with Palestinians, Israelis, Indonesians, Indians, Afghans, and Iranians, my research with psychologists Jeremy Ginges and Douglas Medin finds that offering people material incentives (large amounts of money, guarantees for a life free of political violence) to compromise sacred values can backfire, increasing stated willingness to use violence toward compromise.

This research, supported by the U.S. Department of Defense and the National Science Foundation, shows that backfire effects occur both for sacred values with clear religious investment (Jerusalem, Shariah law) and those with initially none (Iran’s right to nuclear capability, Palestinian refugees’ right of return).

For example, a 2010 study of attitudes toward Iran’s nuclear program found that, for most Iranians, having a nuclear program has nothing sacred about it. But it had become a sacred subject through religious rhetoric for about 13 percent of the population. This group, which tends to be close to the regime, now believes a nuclear program is bound up with the national identity and with Islam itself, so that offering material rewards or punishments to abandon the program only increases anger and support for it.

While sacralization of initially secular issues blocks standard “business-like” negotiation tactics, work with political scientist Robert Axelrod among political leaders in the Middle East and elsewhere indicates that strong symbolic gestures (sincere apologies, demonstrating respect for the other’s values) generate surprising flexibility, even among militants and political leaders, and may enable subsequent material negotiations.

For example, we find that Palestinian leaders and their supporting populations are generally willing to accept Israeli offers of economic improvement only after issues of recognition are addressed. Especially if symbolic gestures are tied to religious notions that are open to interpretation, they may be reframed without compromising their absolute “truth” (for example, rethinking Jerusalem as less a place than portal to heaven, where earthly access to the portal suffices).

Although surprisingly few wars are started by religions, once they start, religion—and the values it imposes—plays a critical role. The Encyclopedia of Wars surveyed 1,763 violent conflicts across history, and only 123 (7 percent) were religious; a BBC-sponsored “War Audit,” which evaluated major conflicts over 3,500 years rated on a 0 to 5 scale for religious motivation (Punic wars = 0, Crusades = 5), found that more than 60 percent had no religious motivation, and less than 7 percent earned a rating greater than 3.

But when conflict is framed by competing religious and sacred values, intergroup violence may persist for decades, even centuries. Disputes over otherwise mundane phenomena then become existential struggles, as when land becomes “Holy Land.”

During protracted intergroup conflict, secular issues tend to become sacralized and non-negotiable, regardless of material rewards or punishments, as with Iran’s nuclear program among regime supporters. In a multiyear study, we found that Palestinian adolescents who perceived strong threats to their people and were highly involved in religious ritual were most likely to see political issues like the right of refugees to return to homes in Israel as absolute moral imperatives, forbidding Palestinian leaders to compromise whatever the costs.

Our work with Greg Berns and his neuroeconomics team suggests that such values become transcendent, emotionally-charged yet stable over time, and processed in the brain as duties bound by rules rather than utilitarian calculations. Neuroimaging also reveals that violations of sacred values trigger emotional responses consistent with sentiments of moral outrage.

The more antagonistic a group’s neighborhood, the more proprietary the group’s sacred values and rituals, increasing in-group reliance, but also disbelief and potential conflict toward other groups. An overview of research by Ginges and colleagues in India, Mexico, Britain, Russia, and Indonesia indicates that greater participation in religious ritual in large-scale societies is associated with greater parochial altruism and, in relevant contexts, support for suicide attacks.

This dynamic is behind the paradoxical reality that the world finds itself in today: Modern multiculturalism and global exposure to multifarious values is increasingly challenged by fundamentalist movements to revive primary group loyalties through greater ritual commitments to ideological purity.

In an age when religious and sacred causes are resurgent, there is urgent need for scientific effort to understand them. Now that humankind has acquired through science the power of God to destroy itself with nuclear weapons, we cannot afford science ignoring religion and the sacred, or scientists simply trying to reason them away. Policymakers should leverage scientific understanding of what makes religion and sacred values so potent a force for both cooperation and conflict, to help increase the one and lessen the other.